In recent years, with the development of chip technologies, such as those for CCD or CMOS, the pixel sizes of chips become smaller and smaller, and the requirement for the imaging quality of the associated optical system becomes higher and higher. As a result, the image pick-up lens system has been developed gradually towards a trend of higher pixel resolution and miniaturization. To adapt to that trend, it is further necessary for the optical lenses mounted on electronic products, such as cell phones or digital cameras, to have a high resolution and other properties.
At present, ordinary high-pixel thin lens systems often employ a five-lens structure. For example, the lens system disclosed in the U.S. Pat. No. 8,411,376B2 comprises the following lenses arranged sequentially from the object side to the image side: a first lens with positive focal power, a second lens with negative focal power, a third lens with negative focal power, a fourth lens with positive focal power, and a fifth lens with negative focal power. Among small aperture diameter configurations, such a system effectively improves the imaging quality while maintaining the miniaturized feature. However, as portable electronic products have been developed well, higher requirements have been put forth for the pixels, imaging quality, and resolution performance, etc. of miniaturized image pick-up lens system. To meet the requirement for high resolution, a large aperture diameter configuration has to be used so that the requirement for illuminance can be met. However, with the known five-lens structure, it is not possible to further shorten the system length and meet the requirement for image quality in a large aperture diameter configuration.
Hence, to meet the requirement for high resolution and high image quality, the present invention provides a six-lens structure, which meets the requirement for high resolution by utilizing a large aperture diameter and ensures miniaturization of the lens system by reducing the lens thickness or the spacing between the lenses; in addition, the present invention further provides an imaging module having the above-mentioned lens system, and a portable terminal having the imaging module, so as to obtain high-quality photographic images.